1. Field of the Invention
The present invention relates to an apparatus for controlling fuel injection timing in a fuel injection pump, in which the fuel injection timing is regulated by the use of a hydraulic timer, an eccentric cam type timer or the like.
2. Description of the Prior Art
U.S. Pat. No. 4,476,832, for example, discloses a fuel injection timing control system for fuel injection pumps in which hydraulic pressure applied to a timer piston of a hydraulic timer is controlled by the regulation of the degree of opening of a solenoid valve to regulate the position of a regulating member for regulating the fuel injection time.
In the disclosed system, since the disc cam comes in contact with the roller inside of the fuel injection pump and a reaction force acts to the roller holder when the plunger of the fuel injection pump is pressed, the system is arranged to avoid the occurrence of resonance in the control system owing to the integer multiple relationship between the period of the change in the magnitude of the reaction force and the pulsation period of the change in the pressure in the high-pressure chamber of the timer caused by the opening/closing operation of the solenoid valve, whereby the time of fuel injection can be controlled in a stable condition.
However, in general, the conventional fuel injection timing control system of this type is arranged in such a manner that the reaction force caused by the fuel injection is applied to the timer piston, whereby the fuel injection time can be advanced or retarded. Consequently, for the disclosed system, it follows that the control gain for retarding the fuel injection time is greater than that for advancing the fuel injection time. This causes a difference in the control response characteristics between the advance control and the retard control of the fuel injection time, and the stability of the control operation will be degraded. This disadvantage arises not only in the use of a hydraulic timer for a distribution type fuel injection pump, but also in the use of a hydraulic timer for a in-line type fuel injection pump.